The present invention relates to a method for protecting buildings against dynamic forces, such as wind or seismic forces, more particularly to a method for anchoring roofs to underlying walls and other building components primarily by utilizing the in-plane strength of the covering xe2x80x9cskinsxe2x80x9d of such components.
The vast number of buildings now built in highly exposed regions and the apparently increasing frequency of category 4 and 5 hurricanes all portend more widespread destruction of houses and other buildings. Much of the destruction is needless. The loss of roofs in particular, with collateral damage to life and property can be preventable.
Many houses and other small buildings in the Caribbean and US xe2x80x9cHurricane Beltxe2x80x9d can lose their roofs to category 3 and 4 storms; much of such stock in the U.S. part of that Belt might be little better built. Weaknesses are common in the tie-down of roof structure to the walls below, and are also found in the inadequacy of the roof framing itself to withstand hurricane uplift forces without breaking.
Several regions now require resistance to category 5 storms for new construction, and indeed it need not be unduly costly to incorporate such resistance during construction. Engineers and builders have established the efficacy of fastening roof structure to exterior wall structure by means of steel straps and the like, which is readily and economically done during construction while the structural members are accessible. Such fastenings are described in more than a dozen U.S. patents, for example in U.S. Pat. No. 4,714,372 entitled HURRICANE TIE, issued to Commins on Dec. 22, 1987, and in U.S. Pat. No. 5,560,156 entitled HURRICANE TIE-DOWN, issued to McDonald on Oct. 1, 1996.
There are millions of houses and other low-rise buildings completed without such fastenings or other adequate reinforcement, and the job of xe2x80x9cretrofittingxe2x80x9d such buildings with steel strap or such devices intended for new construction tends to be disruptive and expensive, even perilous, because trim, soffits, claddings and sheathings must firstly be removed, often working by ladder from the exterior of the building, to access and secure the structural components, after which the whole must be xe2x80x9cmade goodxe2x80x9d. Nevertheless this is the normally recommended approach to such retrofit, apparently based on the notion that roof structural members must be secured directly to wall structural members in order to develop the necessary anchorage of the roof. Methods and apparatus intended for less disruptive retrofitting work are described in several U.S. patents, for example in U.S. Pat. No. 5,319,896 entitled APPARATUS AND METHOD FOR SECURING BUILDING DURING HIGH WIND CONDITIONS, issued to Winger on Jun. 14, 1994, U.S. Pat. No. 5,570,545 entitled APPARATUS FOR HOLDING A ROOF ON A BUILDING DURING HIGH WINDS, issued to Adams on Nov. 5, 1996, and U.S. Pat. No. 5,623,788 entitled ROOF ANCHORING APPARATUS, issued to Bimberg, Uwe and Bimberg, Oliver on Apr. 29, 1997. Several such retrofit measures are essentially cable or strap arrangements or nets that must be skillfully applied to or over the roof each time a storm is anticipated and removed and safely stored after it""s over; others have the advantage of remaining in place as permanent reinforcements but their initial installation is relatively disruptive and costly, and even hazardous in that ladder access is needed as mentioned. Existing buildings are begging for lower cost means of xe2x80x9cadding strength just where neededxe2x80x9d. There is a need for providing a more efficient and less expensive method for protecting buildings, particularly existing buildings and more particularly their roofs, against hurricane force winds.
It is one object of the present invention to provide a retrofitting method for tying roof structures to suitable walls or other building components below the roof structures to enable the roof structures to remain in place in windstormns.
It is another object of the present invention to provide a retrofitting method to strengthen or support roof structural components themselves to help them withstand windstorm forces without breaking.
It is a further object of the present invention to provide a relatively inexpensive retrofitting method for improving building resistance to windstorms.
It is a still further object of the present invention to provide a retrofitting method for improving building resistance to windstorms entailing relatively little disruption of building or occupants.
It is a still further object of the present invention to allow essentially all work to be done safely within the confines of the building while improving building resistance to dynamic forces such as wind or seismic forces.
In general terms there is provided a method for reinforcement of an existing roof structure comprising steps of placing an anchor assembly into a cavity of an existing wall and securing the anchor assembly to the wall coverings enclosing the cavity around the anchorage area, and then tying the anchor assembly to the existing roof structure.
In accordance with one embodiment of the present invention an anchor assembly is inserted into a cavity of a wall underlying a roof structure, the anchor assembly having one or more strong anchor plates extending horizontally across a large portion of the cavity width and thickness, and being attached to cables or other tension members extending upward into the roof space; the anchor plates are made fast within the cavity of the underlying wall by the injection or pouring into the wall cavity of a hardening liquid xe2x80x9cplugxe2x80x9d located to embed and press down upon the upper surface of the anchor plates while strongly adhering to the immediate internal surfaces defining the cavity; and the upper portions of the cables or other tension members are secured to the roof structure in order to hold it down against wind uplift forces.
With respect to another aspect of the invention, a beam or beams are provided to allow the roof to be held down in areas distant from the anchors where the anchors must be spaced widely apart due to the position of suitable underlying walls, said beams normally being installed horizontally within the roof space running transversely to the trusses or rafters and over the anchor points, and being supported (held down) at each anchor point by the aforementioned cables, straps or other tension devices which extend into the roof space; these beams in turn being secured to the roof structure at suitable intervals to hold it down to the underlying components.
With respect to a further aspect of the invention, a roof framing member which is itself weak is tied by strap or other tension tie or strut connecting a relatively central area of the member to an anchor or an anchored beam so that the member is supported against wind uplift forces or xe2x80x9cflutterxe2x80x9d force reversals which might otherwise cause it to fatigue and fail in bending or shear.
With respect to a still further aspect of the invention, a method for reinforcement of existing building structures comprises the steps of: inserting a first anchor assembly into a cavity in a first partition component of the existing building structures; locking the anchor in the cavity and securing the anchor assembly in tension to a building structure adjacent to the first partition component.
It is preferred to insert anchor assemblies into cavities in adjacent partition components which abut each other and to tie the anchor assemblies together so that the building structures are strengthened against tension, compression or shear, resulting from wind or seismic forces.
The method provided according to the invention enables permanent reinforcement of buildings against not only windstorms, but also other dynamic forces, such as seismic forces if it is desired. All work can be done indoors and with a minimum disruption of buildings or people. Other features and advantages will be better understood with reference to the preferred embodiment described below.